This invention relates generally to an apparatus and method for remotely measuring temperature within a passageway, particularly along an interior surface of the passageway. More particularly the invention concerns an apparatus and method for measuring temperature within a human fluid passageway, e.g., a major artery, and determining temperature variations at and around arteriosclerotic plaque within the passageway.
Coronary heart disease takes two forms, a chronic form and an acute form, the latter being the more dangerous because it involves a buildup of unstable plaque within an artery. The unstable plaque is prone to rupture, which often leads to activation of clotting factors in the bloodstream and formation of a blood clot, possibly resulting in a stroke or myocardial infarction. Furthermore, in acute coronary heart disease, sudden death is the first warning sign in up to 25% of cases. Therefore, clinical trials have been conducted to develop a way to diagnose acute coronary heart disease by assessing the nature of the plaque buildup. The trials have indicated that the amount of plaque, the degree of blood vessel narrowing, and the appearance of the plaque under angiography are not helpful in determining the vulnerability of the plaque to rupture. Thus, new ways to identify and manage dangerous vulnerable plaques could add much to the prevention and treatment of life-threatening acute coronary events.
Stable plaques, called atheromas, have thick fibrous caps, smaller lipid cores, and are less likely to rupture. Unstable plaques, on the other hand, are characterized by thin fibrous caps, weakness in the blood vessel wall, and increased inflammatory cells. Angiography and intravascular ultrasound can be used to detect the presence and size of plaque within coronary vessels. These invasive techniques, however, cannot determine the stability and composition of the plaques. Angioscopy, an invasive technique that has shown promise in its ability to detect disruptions in blood vessel linings, is no longer available in the United States. Such invasive techniques carry significant risks and require large bore catheters to accomplish which produce trauma to delicate blood vessels.
Recent investigations have examined plaque temperature as an indicator of plaque instability. Casscells et al. examined blood vessels with plaques taken from human patients who had undergone carotid endarterectomy. Using a thermistor probe with a needle tip, these researchers demonstrated that plaque temperatures varied from 0.5-degrees to 3-degrees C. across the surface of the carotid artery plaques. They concluded that temperature variance was related to the accumulation of macrophages, i.e., inflammatory cells, beneath the plaque cap, with higher temperatures associated with greater macrophage buildup.
Stefanadis et al. measured temperature of plaques using a thermography catheter inserted through a guiding catheter within the coronary vessels. Temperature measurements were taken at five locations near five different vessel lesion sites. Their findings indicate that arteriosclerotic plaques showed greater surface temperatures, with the highest temperatures and greatest variation in temperatures present for patients with unstable angina and myocardial infarction.
The invented device and method provides for measuring temperature within a human fluid passageway, particularly on an inner surface of the passageway in an area of arteriosclerotic plaque, with a minimum degree of risk to delicate blood vessel linings and at a minimum cost for the device. According to the invention, a thermocouple is disposed on a flexible, resilient, and very fine wire lead at a distal portion of the lead, and the lead is inserted through a guidewire with the distal portion of the wire lead extending from a distal end of the guidewire, and the guidewire is inserted percutaneously into the fluid passageway.
The distal portion of the wire lead is formed in an oval, looped or basket shape, having a tip and two or more sides with the thermocouple disposed on one of the sides at a point of maximum outer circumference for the oval shape, and/or on the tip. As the distal portion of the wire lead is slidably moved through the passageway through portions of the passageway having an inner circumference less than the outer circumference of the oval shape, the shape flexes resiliently, biasing the thermocouple against the inner surface of the passageway. Thus, the thermocouple is in direct, biased contact with the inner surface for accurate measurement of the surface temperature, with minimum danger of damage to the blood vessel lining.
The thermocouple at the tip of the looped shape is useful to measure the temperature at areas of near-total or total occlusion where the lead cannot pass and, in areas with less plaque, to measure the temperature in the bloodstream adjacent to the plaque surface. The distal portion of the wire lead may also be formed in an L-shape with the thermocouple disposed at the tip of the L.